Boundary Conditions

Body Force

Analysis ➔ Boundary Conditions ➔ Body Force

This option is used to define Body force for simulation. For Constant Body Force, the vector and magnitude must be specified. By default, the magnitude is 9.81 m/s2. It can be specified in the desired direction using a vector.
Figure 1. Define Constant Body Force in SimLab
For Variable Body Force a time vs acceleration table will be defined. You can either define the table in the Create Table window or import a predefined table (*.txt-file) from other source.
Figure 2. Define Variable Body Force in SimLab

Domain

Analysis ➔ Boundary Conditions ➔ Domain

This tool is used to define the domain and global parameters of the nanoFluidX case.

The vehicle wading case has open boundaries so that the domain size and/or reference values should be defined.

Define Domain Manually is used to specify the final extent of the simulation by defining a bounding box from which the minimum and maximum dimensions (corner points) are calculated.

In addition to the options listed in the Define Box, it is also possible to import files (*.xml) with the coordinates.

For other cases with open boundaries or in case periodic boundary conditions are assigned to the domain, the size of the domain must also be defined manually. These domain parameters are used to define the boundary conditions at minimum and maximum boundary. Options for Boundary Conditions supported are Periodic and Simple Outlet.

The Simple Outlet boundary simply deletes all the particles that cross it.

Selecting Other Options additional parameters can be specified.

AutoDomain

Analysis ➔ Boundary Conditions ➔ AutoDomain

For simple vehicle wading cases, once the vehicle is positioned in the channel, the domain can be created using the AutoDomain tool.
Figure 3.

Alternatively, the vehicle may be positioned in the channel manually using the Move tool. After positioning of the vehicle you can define the Domain using the Domain tool.

Suspension Model

Analysis ➔ Boundary Conditions ➔ Suspension Model

This feature helps to model a simplified vehicle suspension model. With 3-degrees-of-freedom double roller motion, it enhances the fidelity of the water-wading simulations without the need for complex multi-body-dynamics coupling simulation.
Rigid
Rigid suspension models or Double Roller 1DOF Motion is used where fluid forces on the body are negligible, such as shallow cases. In cases where small changes in the road path slope between different segments is small, using the 1DoF variant is sufficient.
Linear Spring/ Damper
Linear spring/damper suspension model or Double Roller 3DOF Motion is recommended only when the modeled linear spring/damper response results in non-negligible differences in body position and angle when passing between different road segments. n double roller 3DoF, the wheels remain rigid and follow the road in the same way as a rigid body motion model while the car body is free to move in the Z direction and rotate about the Y axis. This provides two more degrees of freedom for a total of three, hence double roller 3DoF. Double roller 3DoF is like a half-car model where tire deformation is ignored.
For Double Roller 3DOF Motion, the following quantities are considered:
  • Center of mass: Center of mass of the body phases and reference point used for calculating moments on the body phases. This is the internal center of rotation though apparent center of rotation may be different.
  • Mass: Total mass of the body phases.
  • Moment of inertia (Iyy): Mass moment of inertial of combined body phases about Y.
  • Front spring constant: Effective front wheel spring constant.
  • Rear spring constant: Effective rear wheel spring constant.
  • Front damping constant: Effective front wheel damping coefficient.
  • Rear damping constant: Effective rear wheel damping coefficient.
  • Fluid interaction frequency: Frequency of sampling fluid force and torque on the body phases. The force and torque will remain constant in between sampling points.
  • Heave constraint: Constrain body Z-position by equivalent 1DoF motion. In combination with pitch constraint, it has a similar effect to limiting the stretch/compression of the suspension.
  • Pitch constraint: Constrain body the Y-angle by equivalent 1DoF motion. In combination with heave constraint, it has a similar effect to limiting the stretch/compression of the suspension.

Porous Media

Analysis ➔ Boundary Conditions ➔ Porous Media

  • Name: Impose region name.
  • Region Type: Specifies the type of outlet region.
  • Start Time/ End Time: Specifies the start and finish times which define the window where the impose region is active.
  • Advanced Options: Moving body motion to follow - Impose regions can follow a MOVINGWALL phase with a predefined motion.
  • Other Options: A free text box where additional parameters can be specified.